In operation control of a wind turbine, when the system voltage is decreased, for example, in the event of a power outage, it is operated such that the connection between the wind turbine and the power system is promptly disconnected to prevent a generator and other components from being damaged by overcurrent. On the other hand, for example, in a case of occurrence of a low voltage phenomenon, such as a voltage decrease pattern that is required in LVRT (low voltage ride-through), there is a trend towards standardization such that the wind turbine is continuously operated by maintaining the connection between the wind turbine and the power system.
This is for using electrical power generated by the wind turbine and reactive power for voltage restoration and recovering from frequency fluctuations after recovering from an accident by not disconnecting the wind turbine from the system, even if the system voltage instantaneously drops due to, for example, accidental short circuiting of the power system, if it is within a certain period of time.
In order to accelerate the restoration of the system voltage after the accident, it is important to supply reactive power to the power system. For example, Patent Document 1 discloses a wind turbine generator system that supplies reactive power to the power system during an electrical power drop.    Patent Document 1: U.S. Patent Application, Publication No. 2007/0273155